In an AC electric vehicle that runs by transfer of power or regenerative power supplied from the AC overhead contact line, if a power failure occurs in the AC overhead contact line for any cause, it has been conventionally performed, for security reasons, to detect the power failure of the AC overhead contact line promptly (for example, within 100 to 1000 milliseconds) to stop a controller of the electric vehicle. When a power failure occurs in the AC overhead contact line while the electric vehicle is applying regenerative braking (hereinafter, “regenerative vehicle”) to supply regenerative power to the AC overhead contact line, if there is no electric vehicle that performs power running by receiving supply of power from the AC overhead contact line (hereinafter, “power running vehicle”) within the same substation section, or even if there is the power running vehicle, if the regenerative power supply by the regenerative vehicle does not match with consumed power consumed by the power running vehicle, a fluctuation of current and voltage occurs due to the power failure in the AC overhead contact line. Accordingly, the power failure can be detected by capturing the fluctuation of current and voltage in the AC overhead contact line. However, it has been known that when the regenerative power of the regenerative vehicle and the consumed power of the power running vehicle present in the same substation section become substantially even, a fluctuation range of current and voltage of the AC overhead contact line decreases, thereby making it difficult to detect a power failure. In the following explanations, the power failure of the AC overhead contact line in a state where the regenerative power of the regenerative vehicle and the consumed power of the power running vehicle present in the same substation section become substantially even is referred to as “balanced power failure”.
Conventionally, as a technique of detecting a power failure of an AC overhead contact line, for example, there has been disclosed a technique of detecting a power failure when a current deviation exceeds a predetermined power-failure detection set value, by extracting a current component corresponding to a frequency of the AC overhead contact line (for example, 50 hertz or 60 hertz) from a detection current signal obtained by detecting, for example, an input current of a converter by a current detector, subtracting the detection current signal from an extracted specific-frequency current signal, and comparing a current deviation being a subtraction result with the predetermined power-failure detection set value (for example, Patent Literature 1). Furthermore, there has been disclosed a technique of detecting a power failure by using, for example, an input voltage of a converter, not by using an input current thereof (for example, Patent Literature 2).